This invention relates to a generally square-shaped indexable cutting insert with four cutting edges for mounting in milling cutters for either slotting operations or for left-hand and right-hand face milling of right-angled corners in a metal workpiece.
In prior art milling cutters having square shaped indexable cutting inserts for milling of right-angled corners in a metal workpiece, the cutting inserts are generally mounted in such a way that a reference plane formed by the four cutting edges generates a negative radial rake and a positive axial rake (helix). Each insert has a main cutting edge for milling in a workpiece a right-angled corner, or shoulder, and a transversely directed secondary cutting edge. The secondary cutting edge generally comprises two sections, a section adjacent the main cutting edge that serves as a wiper for forming a smooth base wall of the shoulder and a non-operative section. The cutting insert is designed and mounted in the milling cutter so that a small clearance is formed between the non-operative section and the base wall of the shoulder.
Since the cutting insert is mounted with a positive axial rake it preferably has a positive geometry in order to ensure a clearance between the base wall of the shoulder and the side flank of the insert adjacent the base wall of the shoulder. A cutting insert mounted as described above in a milling cutter would have a relatively small cutting edge wedge angle and a large radial relief angle. Consequently, during machining the cutting insert would be susceptible to breakage in the region of the cutting edge and the milling cutter can also suffer from chatter. It has been found that the cutting insert""s performance can be improved when the clearance between the workpiece and the inserts side flank adjacent the workpiece is reduced in the region of the main cutting edge but is not reduced in the region of the wiper.
Of particular interest are generally square shaped cutting inserts with four cutting edges that can be used for both left-hand and right-hand milling. Such a cutting insert is disclosed in U.S. Pat. No. 5,951,212. However this insert does not provide for improved performance in the manner described.
It is an object of the present invention to provide a novel generally square shaped cutting insert with four cutting edges that can be used for both left-hand and right-hand milling and that provides improved performance in the manner described.
In accordance with the present invention there is provided an indexable cutting insert for use in milling cutters comprising:
a top surface, a bottom surface and M substantially identical side surfaces extending between the bottom surface and the top surface, the top surface having the general shape of an M-sided polygon in a top view of the cutting insert;
each side surface being located between two corner side surfaces;
each side surface sloping outwardly from the bottom surface toward the top surface and intersecting with the top surface at a cutting edge, the cutting edge being located between two corner edges and being substantially parallel to the bottom surface;
each cutting edge comprising a primary cutting edge extending between two wipers, each wiper being adjacent a corner edge;
each side surface comprising at least two component surfaces, a first relief surface adjacent the primary cutting edge and a second relief surface merging with the first relief surface at a boundary line and intersecting with the top surface at the two wipers; wherein
M is an integral multiple of four and the first relief surface has a width dimension measured perpendicularly to the cutting edge, the width dimension having a minimum value proximal to the two wipers and a maximum value at a central region of the cutting edge.
In accordance with the present invention, the first relief surface forms a first non-zero relief angle with a line perpendicular to a reference plane containing the cutting edge associated with each side surface, and the second relief surface forms, in the region of the first and second wipers, a second non-zero relief angle, wherein the second relief angle is greater than the first relief angle.
In accordance with a specific embodiment of the present invention, the boundary line of each side surface comprises two equal substantially straight boundary line sections meeting at a central region of the side surface
Further in accordance with a specific embodiment of the present invention, the second relief surface comprises two similar constituent relief surfaces merging at the central region of the side surface.
Preferably, each one of the two constituent relief surfaces slopes outwardly from the corner side surfaces towards the central region of the side surface.
If desired, the first relief surface is ground.
Further if desired, the two constituent relief surfaces are ground.
Still yet further if desired, the second relief surface is provided with a recess centrally located therein.
In accordance with the present invention the cutting insert has a through bore passing through the top and bottom surfaces.
Preferably, the cutting insert comprises a pressed and sintered powder body.
In accordance with a preferred embodiment of the present invention, M is equal to four. In accordance with an embodiment of the present invention, the second relief surface is provided with a recess centrally located therein.